1. Field of the Invention
This invention relates to thread milling tool. More particularly, this invention relates to thread milling tool that includes a proximal shank portion and a distal cutting portion with a plurality of thread milling teeth having a negative taper angle for creating internal and/or external threads in metallic and other work pieces.
2. Description of the Related Art
Thread cutting tools are known for cutting either internal threads in predrilled holes in a workpiece or external threads on a perimeter of a workpiece. These thread milling tools are typically known as “thread mills”. A typical thread mill has a shank portion and a thread cutting portion. Thread mills generally produce higher quality threaded workpieces when compared to other threading tools, such as taps.
The thread cutting portion of a thread mill may include thread-milling teeth and flutes. A typical thread mill may have between two to four flutes but may include more than four flutes for certain sizes and milling applications. Flutes may be provided on thread mills to provide cutting edges and to channel the chips produced during the milling operation out of a hole that is being threaded. The flutes defined in thread mills may be straight or oriented in a spiral or helical pattern having either a right-handed or a left-handed direction. Straight flutes lie generally parallel to the longitudinal axis of the thread mill extending from the end of the cutting portion and along the cutting portion. Helical or spiral flutes may be defined by a helix angle and wrap around the external surface of the thread mill. As used herein, the helix angle is the constant angle between the spiral flute and the central rotational axis of the cutting tool or any line parallel to the central rotational axis. Those of ordinary skill will understand and may readily determine the helix angle for a particular cutting tool.
The thread-cutting teeth of thread mills may be configured to form threads defined by ISO standards or may have any other thread shape. The thread-cutting teeth have a configuration complementary to that of the threads to be formed on the inner surface of the bore or the external surface of the workpiece. The flutes defined in the cutting portion of the thread mill separate the rows of thread-cutting teeth. The taper angle of the thread milling tool is defined by a successive change in the distance between the central rotational axis of the tool and the crest of individual thread-cutting teeth as the thread-cutting teeth approach the terminal end of the cutting portion of the thread milling tool. A successive decrease in the distance between the central rotational axis of the tool and the crest of individual thread-cutting teeth as the thread-cutting teeth approach the terminal end defines a positive taper angle or forward taper. On the other hand, a successive increase in the distance between the central rotational axis of the tool and the crest on individual thread-cutting teeth as the thread-cutting teeth approach the terminal end defines a negative taper angle or back taper.